Isoflavone rich in soybean food is known as a functional component effective in improving menopausal disorders such as malaise, preventing osteoporosis, preventing hyperlipidemia and arteriosclerosis, preventing breast cancer and prostate cancer and so on. Recent studies have revealed that one of the isoflavones called daidzein is metabolized in vivo by intestinal bacteria into equal, which has stronger estrogen action and antioxidation action. Equal has attracted attention as one of the important active ingredients performing the aforementioned actions in vivo.
In-vivo production of equol from daidzein is not equally performed in all humans and the production ability thereof varies between individuals. It has been reported that 30 to 50% of the humans have equol production ability (Non-Patent Document 1). By such the circumstances, research has been enthusiastically conducted for finding intestinal bacteria having equol production ability and substances accelerating production of equol. Microorganisms having equol production ability that have been so far reported are Bacteroides ovatus, Streptococcus intermedius and Streptococcus constellatus (Patent Document 1). It has been reported that an equol containing egg is obtained by giving a feed containing, e.g., daidzein and a soybean oligosaccharide to domestic fowls (Patent Document 2). A fructo-oligosaccharide (Non-patent Document 2) and twintose (R)(Non-Patent Document 3) have been reported to accelerate production of equol. Note that, Patent Document 1 discloses oligosaccharides such as lacto-oligosaccharide, soybean oligosaccharide, lacturose, lactitol, fructo-oligosaccharide and galacto-oligosaccharide as components contributing to survival and growth of microorganisms having equol production ability. However, each of these carbohydrates is mentioned simply as a nutritional component generally known to contribute to survival and growth of microorganisms; however, no mention is made of how these carbohydrates act upon equol production.
A substance exhibiting estrogen action in vivo is generally called an environmental hormone (endocrine disrupting chemical), which may be involved in reduction of sperm cells and reproduction capacity, and an increase in breast cancer occurrence concerning humans. Isoflavone and equol are each known as one of the phytoestrogens. Excessive intake and excessive in-vivo production of them are likely to have an adverse effect upon humans. Particularly when equol, which has estrogen activity several tens fold as high as other isoflavones, is excessively produced in vivo, it is important to suppress the production of equol. However, examples of microorganisms and substances capable of suppressing the production of equol that have been so far reported are Lactobacillus gasseri (Non-Patent Document 4), insulin (Non-Patent Document 5) and fructo-oligosaccharide (Non-Patent Document 6) alone.
Accordingly, it is very important to appropriately regulate the concentration of equol in-vivo in view of not only treating, improving or preventing various diseases as mentioned above but also avoiding adverse effects caused by the environment hormone-like action of equol. It has been therefore desired to develop a substance having a role in regulating the concentration of equol in vivo and capable of being taken for a long time with high safety.
However, microorganisms and substances capable of regulating the equol concentration in viva are only those mentioned above. Choices are extremely limited and their effects are insufficient. In addition, there have been no reports on a selective medium for a microorganism having conversion ability to equol. In the circumstances, it has been strongly desired to develop a selective medium for simply and quickly screening a microorganism having conversion ability to equol and detecting a microorganism having conversion ability to equol in a specimen.
[Patent Document 1] WO99/7392
[Patent Document 2] JP-A-2003-310177
[Non-Patent Document 1] Proc Soc Exp Biol Med, Vol. 217, No. 3, p 335-339 (1998)
[Non-Patent Document 2] J Nutr, Vol. 132, p 2048-2054 (2002)
[Non-Patent Document 3] Summary of lectures of 2005 annual meeting of the Japanese Society for Bioscience Biotechnology and Agrochemistry, p 97 (2005)
[Non-Patent Document 4] Food Research Organization Information, No. 17, p 18-19 (2005)
[Non-Patent Document 5] J Agric Food Chem, Vol. 52, No. 10, p 2827-2831 (2004)
[Non-Patent Document 6] Arch Microbiol, Vol. 183, No. 1, p 45-55 (2005)